Sick or malnourished Pekin? (Pictures)

Hi all! I'm a chicken girl, but is been researching ducks when a friend of mine asked me to take 2 rescue Pekins three weeks ago. We have a large ponds and my husband made them a shelter out of pallets, so we got them. I named them Johnny and June. June went Broody 3 weeks ago. So far she is an excellent broody duck.

Cut to last night. Same friend called me and said someone had dumped out a duck at the pond she does her Herpetology studies at three days prior and the duck hadn't moved. She brought me the duck.

The ducks eyes were droopy, like a basset hound. Filthy. It seems puffed up. The duck began eating and drinking quickly and hasn't stopped. I'm not sure how old it is, or if it's male or female. I am leaning towards female. Especially because of how my drake reacted to it. I'm a total train wreck here, guys. I do know that it is just in the process of getting in its flight feathers. Its voice is still pretty squeaky. It's in pretty bad shape. Dirty. Hasn't been preening itself. The droopy eyes have gotten better, but not totally gone.

Aside from those things I can't find anything else wrong. I kept it in a kennel last night and my drake, Johnny, found it this morning and she puffed up a bit when she saw him, but they got along well after that. He stayed by her in the kennel for hours. I finally let it out of the kennel and it went down to the pond and stares searching in the mud and drinking water.

I feed them a mix of flock feed- 16% protein I believe, 6-way, Brewer yeast, diatomaceous earth, and oats. They forage, too. I've fried to get them to eat leafy greens- romane, kale, shredded broccoli with no luck. They are very picky. I don't have that problem with my chickens. Any pointers?